Ultrasonic non-destructive pulse testing apparatus is known in which an ultrasonic transducer is pulse driven to apply ultrasonic pulses to an object to be tested, and received signals corresponding to variations or defects in the object are displayed on a cathode-ray tube (CRT) and used to actuate indicating apparatus such as an alarm, marker, recorder, etc. Commonly the received signals are echoes reflected back from the front and rear surfaces of the object, and from flaws, defects, discontinuities or other variations in the object between front and rear surfaces.
A single ultrasonic transducer is often used for transmission and reception, although separate transducers may be employed. Instead of receiving echoes, transmitter and receiving transducers may be placed on opposite sides of the object, and changes in the received signals used to detect variations or defects in the object. To facilitate applying the ultrasonic pulses to the object, and receiving signals therefrom, a couplant such as water, oil, etc. is usually introduced between the transducer(s) and the object under test. Relative movement between transducer(s) and object may be used to scan various portions of the object.
In such apparatus highly stable driving pulses are important. It is also desirable to provide a range of PRF's (pulse recurrence frequencies) in order to meet various requirements encountered in practice. Thus thicker objects may require lower PRF's than thinner objects since it will take longer for the ultrasonic waves to pass through the object. At each PRF, however, stability should be maintained.
Received signals may be very small, perhaps 1 or a few microvolts. Consequently high amplification is necessary, and high stability with low noise level is important, as well as adequate bandwidth to enable very short high frequency driving pulses to be employed.
Signals gates have been described which utilize a delayed transmitter pulse, or a front surface pulse, to start the gate. The gates may be used to select echoes in a region of interest within the object for actuating an alarm when the echoes exceed a threshold level. It has been suggested to display such gates on the same sweeps as the echoes, in which case the echoes ride on the top or bottom of the gate, depending on the gate polarity. Also, any noise present will also ride on the gate. This increases the difficulty in measuring the echo amplitude, since the gate amplitude must be taken into account. It has been suggested to display the received echoes and gate on alternate sweeps, particularly with the gate baseline offset from the sweep baseline and echoes within the gate displayed on the gate.
Expanded sweeps have been suggested for displaying an expanded portion of the complete echo signal on the face of the CRT. Such expansion may cause the desired portion to move off the screen, thus requiring further adjustment.
Time markers impressed on the sweeps have also been suggested, either on the same sweeps as the echoes or on alternate sweeps.
The present invention is directed to the provision of ultrasonic pulse testing apparatus having improved means for generating driving pulses, amplifying received signals, displaying the received signals and signal gate with marker pulses, and producing expanded sweeps.